1 files changed, 30 insertions, 12 deletions

diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index d27f767..215431c 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -9546,14 +9546,32 @@ bool SpecialMemberDeletionInfo::shouldDeleteForSubobjectCall(
   CXXMethodDecl *Decl = SMOR.getMethod();
   FieldDecl *Field = Subobj.dyn_cast<FieldDecl*>();
 
-  int DiagKind = -1;
-
-  if (SMOR.getKind() == Sema::SpecialMemberOverloadResult::NoMemberOrDeleted)
-    DiagKind = !Decl ? 0 : 1;
-  else if (SMOR.getKind() == Sema::SpecialMemberOverloadResult::Ambiguous)
-    DiagKind = 2;
+  enum {
+    NotSet = -1,
+    NoDecl,
+    DeletedDecl,
+    MultipleDecl,
+    InaccessibleDecl,
+    NonTrivialDecl
+  } DiagKind = NotSet;
+
+  if (SMOR.getKind() == Sema::SpecialMemberOverloadResult::NoMemberOrDeleted) {
+    if (CSM == CXXSpecialMemberKind::DefaultConstructor && Field &&
+        Field->getParent()->isUnion()) {
+      // [class.default.ctor]p2:
+      //   A defaulted default constructor for class X is defined as deleted if
+      //   - X is a union that has a variant member with a non-trivial default
+      //     constructor and no variant member of X has a default member
+      //     initializer
+      const auto *RD = cast<CXXRecordDecl>(Field->getParent());
+      if (RD->hasInClassInitializer())
+        return false;
+    }
+    DiagKind = !Decl ? NoDecl : DeletedDecl;
+  } else if (SMOR.getKind() == Sema::SpecialMemberOverloadResult::Ambiguous)
+    DiagKind = MultipleDecl;
   else if (!isAccessible(Subobj, Decl))
-    DiagKind = 3;
+    DiagKind = InaccessibleDecl;
   else if (!IsDtorCallInCtor && Field && Field->getParent()->isUnion() &&
            !Decl->isTrivial()) {
     // A member of a union must have a trivial corresponding special member.
@@ -9569,13 +9587,13 @@ bool SpecialMemberDeletionInfo::shouldDeleteForSubobjectCall(
       //     initializer
       const auto *RD = cast<CXXRecordDecl>(Field->getParent());
       if (!RD->hasInClassInitializer())
-        DiagKind = 4;
+        DiagKind = NonTrivialDecl;
     } else {
-      DiagKind = 4;
+      DiagKind = NonTrivialDecl;
     }
   }
 
-  if (DiagKind == -1)
+  if (DiagKind == NotSet)
     return false;
 
   if (Diagnose) {
@@ -9593,9 +9611,9 @@ bool SpecialMemberDeletionInfo::shouldDeleteForSubobjectCall(
           << /*IsObjCPtr*/ false;
     }
 
-    if (DiagKind == 1)
+    if (DiagKind == DeletedDecl)
       S.NoteDeletedFunction(Decl);
-    // FIXME: Explain inaccessibility if DiagKind == 3.
+    // FIXME: Explain inaccessibility if DiagKind == InaccessibleDecl.
   }
 
   return true;